bpf: Refactor mark_{dynptr,iter}_read

There is possibility of sharing code between mark_dynptr_read and
mark_iter_read for updating liveness information of their stack slots.
Consolidate common logic into mark_stack_slot_obj_read function in
preparation for the next patch which needs the same logic for its own
stack slots.

Acked-by: Eduard Zingerman <[e-mail]>
Signed-off-by: Kumar Kartikeya Dwivedi <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

kernel/bpf/verifier.c

···
 	return 0;
 }
 
-static int mark_dynptr_read(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
+static int mark_stack_slot_obj_read(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
+				    int spi, int nr_slots)
 {
 	struct bpf_func_state *state = func(env, reg);
-	int spi, ret;
+	int err, i;
+
+	for (i = 0; i < nr_slots; i++) {
+		struct bpf_reg_state *st = &state->stack[spi - i].spilled_ptr;
+
+		err = mark_reg_read(env, st, st->parent, REG_LIVE_READ64);
+		if (err)
+			return err;
+
+		mark_stack_slot_scratched(env, spi - i);
+	}
+	return 0;
+}
+
+static int mark_dynptr_read(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
+{
+	int spi;
 
 	/* For CONST_PTR_TO_DYNPTR, it must have already been done by
 	 * check_reg_arg in check_helper_call and mark_btf_func_reg_size in
···
 	 * bounds and spi is the first dynptr slot. Simply mark stack slot as
 	 * read.
 	 */
-	ret = mark_reg_read(env, &state->stack[spi].spilled_ptr,
-			    state->stack[spi].spilled_ptr.parent, REG_LIVE_READ64);
-	if (ret)
-		return ret;
-	return mark_reg_read(env, &state->stack[spi - 1].spilled_ptr,
-			     state->stack[spi - 1].spilled_ptr.parent, REG_LIVE_READ64);
+	return mark_stack_slot_obj_read(env, reg, spi, BPF_DYNPTR_NR_SLOTS);
 }
 
 static int mark_iter_read(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
 			  int spi, int nr_slots)
 {
-	struct bpf_func_state *state = func(env, reg);
-	int err, i;
-
-	for (i = 0; i < nr_slots; i++) {
-		struct bpf_reg_state *st = &state->stack[spi - i].spilled_ptr;
-
-		err = mark_reg_read(env, st, st->parent, REG_LIVE_READ64);
-		if (err)
-			return err;
-
-		mark_stack_slot_scratched(env, spi - i);
-	}
-
-	return 0;
+	return mark_stack_slot_obj_read(env, reg, spi, nr_slots);
 }
 
 /* This function is supposed to be used by the following 32-bit optimization